Sacrificial materials are commonly used in fabrications of microstructures such as microelectromechanical systems and semiconductor devices. Specifically, sacrificial layers having selected sacrificial materials are deposited between adjacent structural layers (e.g. between vertically disposed and laterally disposed structural layers) of the microstructures. A typical and pervasively used sacrificial material is amorphous silicon. Once the desired structure of the microstructure is formed, the sacrificial layers are removed by etching and the structural layers are left behind.
The success of the etching process depends upon the selectivity of the etching process, wherein the selectivity is defined as the ratio of the amount of the sacrificial material being removed to the amount of the materials of the structural layers being removed. Performance, uniformity and yield can all be improved with increase in the etch selectivity.
More recently, etching methods using selected vapor phase etchants have exhibited many advantages, such as high selectivity, less contamination and less process stiction in fabrications of microstructures as opposed to other available etching methods, such as wet etching techniques.
Accordingly, a method and apparatus is desired for removing sacrificial materials, especially the sacrificial material between vertically disposed structural layers in microstructures using selected vapor phase etchant with high efficiency and selectivity.